class_docstr: Unit tests for the LangChain wrapper LLM class
code: def prompt(self):
      class MockAbstractPrompt(AbstractPrompt):
          template: str = "Hello"
  
      return MockAbstractPrompt()
  
file_path: pandas-ai/tests/llms/test_langchain_llm.py
imports: from langchain.llms import OpenAI
  import pytest
  from pandasai.llm import LangchainLLM
  from pandasai.prompts import AbstractPrompt
  from unittest.mock import Mock
label_desc: Use image node_id 2 for calling the TestLangchainLLM obj's underlying member method code with example usage: obj.prompt() and returns: MockAbstractPrompt